A micro-fluid ejection device such as a thermal ink jet printer, forms an image on a printing surface by ejecting small droplets of ink from an array of nozzles on an ink jet printhead as the printhead traverses the print medium (for scanning type printheads). The fluid droplets are expelled from a conventional thermal micro-fluid ejection head when a pulse of electrical current flows through the fluid ejection actuator, which is a resistive fluid ejection actuator, vaporizing a small portion of the fluid to create a bubble that expels such a drop(s) from a nozzle positioned above the resistive fluid ejection actuator. Typically, there is one resistive fluid ejection actuator corresponding to each nozzle of a nozzle array on the ejection head. The resistive fluid ejection actuators are activated under the control of a microprocessor in the controller of the micro-fluid ejection device.
Resistive fluid ejection actuators are prone to mechanical damage from cavitation as the bubble collapses after drop ejection. Any non planar topography near the actuator pad, particularly at the edges of the pad where conductor lines may terminate, can act as a stress riser for conformal overcoats or films that are applied to protect the actuator pad. Non-planar topographies can also cause non-homogenities in any overcoats or films. Such non-homogenities may also result from the thermal gradient between the relatively hot center of the resistive actuator pad and the relatively cool edges.
With reference to FIG. 1, there is shown a conventional structure 10 for a resistive fluid ejection actuator, in the form of a resistive heater, for a micro-fluid ejection head. In this structure 10, there is provided a substrate 12 having a thermal barrier 13 having a resistive layer 14 deposited thereon. The resistive layer 14 is in electrical contact with a conductor layer 16. The conductor layer 16 is etched to create a heater pad area 18 between conductive portions 16A and 16B. As the conductor layer 16 is relatively thick (e.g., about 5000 Angstroms), a subsequent dielectric layer 20 and cavitation layer 22 must step up at the edges of the heater pad area 18 to cover and seal exposed portions of the conductive portions 16A and 16B. This step up results in a non-planar structure as shown. Additional layers, such as an insulating layer 24 and a passivation layer 26 are conventionally included to complete the heater structure 10.
The mechanical, cavitational, thermal, and other stresses associated with this conventional non-planar structure 10 can collectively result in weak areas in the film or overcoat layers 20-26 that are prone to fracture, causing pre-mature failure of the actuator. As the overcoats and films become thinner, such as in an effort to increase thermal efficiency, the likelihood of such weak areas in such layers increases.
The foregoing and other needs may be provided for by a fluid ejection actuator that is provided by a conductive layer adjacent a substrate. The conductive layer has a substantially nonconductive portion. The substantially non-conductive portion includes a portion of the conductive layer that has been treated to have low conductivity properties. A resistive layer is adjacent the conductive layer. The substantially non-conductive portion of the conductive layer substantially defines the fluid ejection actuator. Such an actuator might be particularly suitable for use as a micro-fluid ejection head.
In another one of the embodiments, the disclosure relates to a method for manufacture of a resistive fluid ejection actuator. In one such method, a conductive layer is applied adjacent a substrate. A mask is applied over the conductive layer and developed to expose a selected portion of the conductive layer. The exposed selected portion of the conductive layer is treated to transform the selected portion into a portion having low conductivity properties to provide a substantially non-conductive portion. The mask is removed. A resistive layer is applied adjacent the conductive layer to provide a fluid ejection actuator. Still further embodiments exist.
The embodiments described herein improve upon the prior art in a number of respects. For example, at least some of the embodiments lend themselves to a variety of applications in the field of micro-fluid ejection devices, and particularly in regards to inkjet printheads having improved longevity and less susceptibility to mechanical failure. Another advantage of at least some of the embodiments described herein is that thinner protective layers may be used that may be effective to increase the energy efficiency of the fluid ejector actuators.